The present invention relates to magnetic tape transports, and more particularly, to a mechanism for insuring proper threading of a leader block of a tape cartridge along a tape path to a take-up hub.
One magnetic tape cartridge particularly suited for storing digital data is defined in Proposed American National Standard (ANSI) X3B5/87-238. This tape cartridge contains a single reel of magnetic tape including a leader block for interfacing with an automatic threading system and is hereafter referred to as the "leader block tape cartridge." This cartridge is further illustrated and described in U.S. Pat. Nos. 4,335,858; 4,334,656; 4,383,660 and 4,452,406.
A number of tape transports have been developed that utilize the aforementioned leader block tape cartridge. One example is the IBM (Trademark) 3480 tape transport. Such drives include a mechanism for extracting the leader block, threading the tape and re-inserting the leader block back into the tape cartridge. The corner of the tape cartridge housing has a receptacle defined by upper and lower walls for removably receiving the leader block therein. This leader block is connected to the terminal end of a length of half-inch magnetic tape wound about a supply reel within the cartridge housing. Heretofore, tape transports for the leader block tape cartridge have typically utilized a threader pin whose narrow upper portion is received in the smaller upper portion of a cylindrical aperture formed in the leader block upon insertion of the cartridge into the drive. The pin or cartridge is then moved vertically so that its enlarged lower portion is captured in the lower enlarged portion of the aperture in the leader block. Thereafter the threader pin is moved horizontally by an articulated rotating arm or a guide belt to pull the leader block and the tape connected thereto along a tape path until the leader block is received in a slot formed in a take-up hub. The read/write head and take-up hub are positioned above a horizontal deck plate which typically forms a part of the frame of the tape drive.
One example of a leader block extraction, threading and insertion mechanism of the foregoing type is disclosed in U.S. Pat. No. 4,704,645 assigned to Cipher Data Products, Inc. See also U.S. Pat. Nos. 4,334,656; 4,335,858; 4,399,936; and 4,608,614 assigned to IBM, U.S. Pat. No. 4,679,747 assigned to Laser Magnetic Storage International Company and U.S. Pat. No. 4,742,407 assigned to Aspen Peripherals for further examples. Similar extracting, threading, and insertion arrangements for tape cartridges analogous to the leader block tape cartridge are shown in U.S. Pat. Nos. 4,477,851 and 4,646,177.
The magnetic tape in the leader block tape cartridge has an oxide side and a MYLAR (Trademark) side. For some time, it was assumed that any tape guide rollers could only contact the MYLAR side of the tape or else errors would be induced in the reading or writing of data on the tape. This has led to the use of complicated zig-zag tape paths and the requirement for the aforementioned complex articulated arms and timing belts for threading the leader block along a tape path. However, these complex mechanims are difficult to fit within the confines of a drive that meets the industry standard eight-inch form factor, and even more difficult to fit within a tape drive that meets the industry standard five and one-quarter-inch form factor. They are also subject to malfunctions and to wide variations in tolerances which are unacceptable in very high density recording. The MICROSTREAMER (Trademark) reel-to-reel streaming tape drive sold by Cipher Data Products, Inc. has successfully utilized tape guide rollers that contact the oxide side of the tape without inducing errors. See U.S. Pat. No. 4,243,186 granted Jan. 6, 1981 to Barton et al.